DESCRIPTION (adapted from the application) Since the early 1980s, enterohemorrhagic Escherichia coli (EHEC) has been recognized as a cause of diarrhea and hemorrhagic colitis. The most serious complication of EHEC infection is hemolytic uremic syndrome (HUS), which occurs primarily in children. While it is now recognized that EHEC strains belonging to a variety of serotypes can cause HUS, O157:H7 is the dominant EHEC serotype in many parts of the world and has been the type most commonly associated with foodborne outbreaks. EHEC O157:H7 virulence determinants include shiga toxins (Stx), a chromosomal pathogenicity island called the locus for enterocyte effacement (LEE) that encodes the adhesin intimin and mediates attaching and effacing (AE) activity, as well as a hemolysin (HlyA), a serine protease (EspP), and an plasmid-encoded adhesin with homology to the Clostridium difficile toxin B (Efal). We have developed a mouse model of Citrobacter rodentium colitis that is dependent on LEE-encoded gene products and AE activity for colonization. In this model, suckling mice develop significant mucosal damage in the colon, which is associated with severe colitis and death. Adult mice, on the other hand, develop colonic epithelial hyperplastic and a milder colitis that is typically subclinical. We have recently discovered that an increased inoculum of C. rodentium (10-9 CFU, intragastric) leads to significant mucosal damage and severe colitis in adult mice. We now propose to develop a mouse model of AE colitis for O157:H7 by introducing individual virulence determinants from EHEC O157:H7 into C. rodentium and using these strains to infect adult mice. Specifically, we will 1) characterize the role of O157: H7 intimin in this mouse model of AE colitis, 2) characterize the role of Stx in this mouse model of AE colitis, and 3) characterize the mucosal response to O157:H7 intimin and to Stx in vitro and in vivo. Overall, this work will allow us to test the hypothesis that AE-dependent mucosal damage and colitis influence Stx translocation from the gut. It should also lead to the development of a mouse model for studies of O157:H7 pathogenesis and for testing preventive and therapeutic approaches directed against this important foodborne illness.